The present invention relates to swivel wheel casters, and in particular to a plastic swivel wheel caster having a plastic fork assembly formed around a bearing assembly with a top-plate engaging the bearing assembly held securely in place by a retention plug inserted into the top plate through the bearing assembly.
Caster wheel assemblies are well known in the prior art and have been widely used on very diverse apparatuses. Casters are found on weight bearing legs of tables, chairs, and other furniture. They are found on the bases or undersides of flat bottomed furniture such as bookshelves, television, and entertainment stands. Casters are also found on baby carriages, carts, and moving equipment. Unfortunately, caster assemblies frequently get fouled by grit, dirt, hair and other particles in the environment. These particles result in substantial wear and tear leading to caster wheel assembly breakdown. Also, caster assemblies frequently break or fall apart.
Conventional casters include wheel assemblies having a cylindrical extension which rotatably engages a hollow tubular sleeve disposed on a weight bearing leg of an apparatus, wheel assemblies having openings or hollow sleeves for rotatably receiving a cylindrical extension disposed on an apparatus, and similar modifications thereof. Numerous examples of such apparatuses are found in the patent literature including U.S. Pat. No. 1,559,078 issued to Everly (a caster wheel assembly having a fork with a cylindrical extension disposed opposite the wheel and rotatably engaged in a hollow sleeve inserted in the leg of a piece of furniture), U.S. Pat. No. 5,390,394 issued to Huang (a detachable front wheel assembly having a frame attachment member with a hollow sleeve for rotatably receiving a tubular extension disposed opposite the wheels for use as the front wheel assembly of a stroller), U.S. Pat. No. 5,408,723 issued to Juliean et al. (a swivel wheel assembly having a tube plugxe2x80x94hollow sleevexe2x80x94inserted in a hollow leg for receiving a pin rotatably engaged in a rotary member having wheels attached thereto), U.S. Pat. No. 5,361,454 issued to Sumser et al. (a snap-on swivel wheel assembly having a wheel supporting unit with a hollow tube sleeve for rotatably receiving a tubular sleeve having a bottom with an opening and a fastener attaching the two sleeves together; the tubular sleeve in turn rigidly receives a weight bearing leg of a baby carriage), and U.S. Pat. No. 4,897,895 issued to Wang (a caster device having a wheel supporting fork with a hollow tube sleeve for rotatably receiving a tubular sleeve having flexible detents to prevent separation which tubular sleeve in turn rigidly receives a weight bearing leg of a baby carriage).
It is also known in the art to use ball bearings in caster wheel assemblies. U.S. Pat. No. 5,199,131 issued to Harris teaches a caster assembly having a stem and ball bearing retainer made of a single homogeneous unit of reinforced plastic, a horn made of a single piece of reinforced plastic, a bottom bearing retainer made of a single piece of reinforced plastic, an upper set of ball bearings between the horn and the upper retainer, a lower set of ball bearings between the horn and the bottom retainer, with the bottom retainer being ultrasonically welded to the unitary stem and retainer. Similarly, U.S. Pat. No. 627,108 issued to Fishel describes a caster assembly which utilizes exposed ball bearing sets. The ball bearing sets of these inventions are not protected from environmental factors, may become entangled with debris, and therefore, are susceptible to heightened wear and tear which reduces the overall life span the caster assembly.
Other bearings have also been used with casters. U.S. Pat. No. 4,653,139 issued to Vollberg et al. discloses a caster with a plain thrust bearing between the wheel frame and the frame carrier. The invention therein has a bifurcated frame for the wheel and the carrier which defines a plain thrust bearing, and allows the frame to swivel relative to the carrier about an axis extending at right angles to the axis of the wheel. A ring-shaped coupling prevents the separation of the frame and carrier whose abutting surfaces are engaged by the ring-shaped coupling.
Other prior art inventions utilize posts and the like which engage part of the caster assembly and are held in place by flanges, retainer rims, and other devices but do not make use of ball bearings. U.S. Pat. No. 4,509,227 issued to Keane discloses a three-piece swivel caster having a force transfer roller which has a mounting portion with a post that engages a base and is held therein by flanges. Keane does not disclose the use of a plug to insure that the post does not disengage from the base. Also, U.S. Pat. No. 4,953,257 issued to Seynhaeve describes a caster wheel having a means for capturing and holding a rim by use of a brace snapped into the bore of the rim which is mated with an axis that prevents separation. Furthermore, U.S. Pat. No. 1,395,484 issued to Diss describes a caster wheel having a means for capturing and holding a rim by use of a U-shaped retainer spring strip but the caster slidably rotates. All three of these inventions do not use ball bearings but are instead slidably engaged in a retainer mechanism.
Snap engaging fastener systems for providing rotary motion are also known in the art, as shown in U.S. Pat. No. 5,143,500 issued to Schuring et al. Schuring et al. discloses a fastener system having a stud element with a split or bifurcated head, forming two prongs, that fits inside a socket sleeve. The socket sleeve and stud element are thereby slidably engaged to permit rotation but not disengagement. The invention of Schuring et al. does not disclose the use of ball bearings.
None of the above inventions and patents, taken either singularly or in combination, is seen to describe the instant invention as claimed.
An object of the present invention is to provide a snap-fit caster wheel assembly which is lighter than conventional casters which are predominantly fashioned from metals and is sturdier than prior art plastic casters. The present caster wheel assembly is composed predominantly of plastic and therefore is much lighter than conventional casters but its configuration is much sturdier.
Another object of the invention is to provide a snap-fit caster wheel assembly which limits hair, grit or other particles from getting trapped in the wheel assembly and thereby assuring free horizontal rotation of the fork and wheel of the caster assembly.
Yet another object of the present invention is to provide a snap-fit caster wheel assembly which is designed to last for the life of the apparatus to which the caster is attached. The bearing assembly of the present invention, which facilitates the horizontal rotation, is protected from environmental exposure and has few parts. These qualities assure a longer life for the wheel assembly.
The present invention relates to a plastic caster comprising a fork assembly having a bearing housing portion, at least one prong rigid with the housing portion with at least one wheel mounted on the prong for rotation about a first axis. The bearing housing portion is formed around a bearing assembly. The bearing assembly has inner and outer ring-shaped raceways, preferably with bearings evenly dispersed in a cage between the inner and outer raceways. The housing portion is formed such that the outer raceway is securely affixed to the housing portion while the inner raceway rotates freely about a second axis which is substantially normal to the first axis. The housing portion further comprising a first surface which is remote from the first axis.
A top-plate has a second surface which abuts the first surface. The top-plate has an extension extending from the second surface with an opening therein. The extension engages the inner raceway permitting the top plate and fork assembly to independently rotate about the second axis. A retention plug is mated with the opening of the extension preventing disengagement of the top-plate from the inner raceway to securely attaching the top-plate to the inner raceway.
An advantage of the invention is to provide a caster wheel assembly having fewer parts than commonly found in casters. The present caster has only three separate parts therefore assembling the present caster is easier than assembling casters with more parts.
Another advantage of the present invention is that it does not fall apart easily, and will remain intact for a long time. Conventional casters have the unfortunate disadvantage of coming apart and bending requiring replacement. The present casters are unlikely to come apart and cannot bend as metal casters do.
These and other objects of the present invention will become readily apparent upon further review of the following drawings and specification.